Here, \(R^{(0)},L^{(0}\) , \(R^{(1)},L^{(1)}\) , and \(R^{(2)},L^{(2)}\)  are
field-independent, linear, and quadratic in the dynamical variables.
The interaction is consistent if all the gauge symmetries and gauge
identities of free model are preserved by the deformation of
equations of motion. Equation (8) of paper [1]} provides
a simple formula for computation of physical degrees of freedom
number based on the orders of derivatives involved into equations of
models, gauge symmetries, and gauge identities. The free and
non-linear theory must have one and the same number of physical
degrees of freedom.
